Piston for an internal combustion engine

ABSTRACT

The present invention relates to a piston ( 10 ) for an internal combustion engine, having an outer circumferential cooling channel ( 19 ) and an inner cooling cavity ( 21 ), the cooling cavity bottom ( 22 ) of which has an opening ( 23 ) that is closed off with a separate closure element ( 33 ) that has at least one cooling oil opening ( 35 ), whereby the closure element ( 33 ) is held, in clamped manner, by means of two engagement elements ( 37 ) disposed on the outer edge, in at least one engagement groove ( 34 ) provided in the region of the opening ( 23 ) of the cooling cavity bottom ( 22 ). According to the invention, it is provided that the closure element ( 33 ) has at least two spring tabs ( 38 ) that support themselves on a contact surface ( 39 ) provided in the piston interior, in each instance, in such a manner that the closure element ( 33 ) is held in the engagement groove ( 34 ) under axial bias.

The present invention relates to a piston for an internal combustion engine, having an outer circumferential cooling channel and an inner cooling cavity, the cooling cavity bottom of which has an opening that is closed off with a separate closure element that has at least one cooling oil opening, whereby the closure element is held, in clamped manner, by means of two engagement elements disposed on the outer edge, in at least one engagement groove provided in the region of the opening of the cooling cavity bottom.

A piston of this type is disclosed in DE 10 2008 055 908 A1. The known closure element serves to close off the opening in the cooling cavity bottom in such a manner that cooling oil can flow out of the inner cooling cavity, in the direction of the piston pin, in controlled manner, in order to lubricate the piston pin. It is problematic, in this connection, that the known closure element is not always reliably held in its seat during engine operation, because of the forces that act on it during the piston stroke.

The task of the present invention consists in further developing a piston of this type in such a manner that the closure element is reliably secured in its position, relative to the forces that act on it during the piston stroke.

The solution consists in that the closure element has at least two spring tabs that support themselves on a contact surface provided in the piston interior, in each instance, in such a manner that the closure element is held in the engagement groove under axial bias.

The embodiment according to the invention makes it possible to reliably and effectively close off the opening in the piston crown, with regard to forces that are in effect during the piston stroke. Fluttering of the closure element is avoided. This is brought about in that a spring bias is in effect between the spring tabs and the engagement elements in the assembled state. This spring bias acts in the axial direction and stabilizes the closure element in its seat, with regard to the forces that are in effect during the piston stroke. The spring bias can be adjusted in known manner, by way of the thickness of the entire closure element or individual regions of it, and/or by way of beads introduced into the closure element.

Advantageous Further Developments are Evident From the Dependent Claims.

A preferred embodiment provides that the spring tabs support themselves on a contact surface provided in the region of the pin boss links, in each instance. In this region, surface region formed in the pin bosses can serve as a contact surface. In this case, it is practical to provide the at least one engagement groove also in the region of the pin boss links, in order to achieve an optimal spring bias.

The at least two engagement elements and/or the at least two spring tabs preferably lie diametrically opposite one another. The most advantageous force distribution is guaranteed by this arrangement.

The engagement elements are preferably configured as engagement tongues. Such engagement tongues are very flexible and effective as springs.

The closure element preferably has two or more cooling oil openings, so that a very precisely metered amount of cooling oil can flow off, out of the inner cooling cavity, in the direction of the piston crown. The closure element can be produced from any desired material, whereby a spring steel sheet has proven to be well suited.

The at least one cooling oil opening in the closure element can be configured as a usual round opening or, for example, also as a slit that extends inward from the edge of the closure element.

The engagement elements and/or the spring tabs can be delimited by slits that extend radially inward, which extend inward from the edge of the closure element and also serve as cooling oil openings. At the same time, the flexibility of the engagement elements and the spring tabs is increased.

Furthermore, a narrow gap can be provided in the region of the spring tabs, between the piston interior and the closure element, which gap can also serve to control the cooling oil flow.

The opening in the cooling cavity bottom and the closure element are generally configured to be round. If the opening in the cooling cavity bottom is configured to be oval or as an oblong hole, it is practical if the closure element has a shape that corresponds to this.

The piston according to the invention can be configured as a one-part piston. It can also be produced from an upper piston part and/or the lower piston part. These can be cast parts or forged parts, and can be produced from a steel material, for example. Friction welding, for example, is a good possibility as a joining method.

An exemplary embodiment of the invention will be explained in greater detail below, using the attached drawings. These show, in a schematic representation, not true to scale:

FIG. 1 an exemplary embodiment of a piston according to the invention, in section;

FIG. 2 the piston according to FIG. 1, in a representation rotated by 90°, in section;

FIG. 3 the piston according to FIG. 1 in a view from below;

FIG. 4 the closure element for the piston according to FIG. 1;

FIG. 5 a perspective view of the piston according to FIG. 1 with the inserted closure element according to FIG. 4, partly in section;

FIG. 6 an enlarged partial representation of the closure element according to FIG. 5.

FIGS. 1 to 3 show an exemplary embodiment of a piston 10 according to the invention, which is forged from a steel material in the exemplary embodiment. In the exemplary embodiment, the piston 10 according to the invention is a multi-part piston and is composed of an upper piston part 11 and a lower piston part 12. The upper piston part 11 forms a wall region 13 a of a combustion bowl 13, a circumferential top land 14, and a circumferential ring belt 15 having ring grooves for accommodating piston rings. The lower piston part 12 has a piston skirt 16 having pin bosses 17 and pin boss links 18. The pin bosses 17 are provided with pin bores 17 a for accommodating a piston pin. The lower piston part furthermore forms the crown region 13 b of the combustion bowl 13. The upper piston part 11 and the lower piston part 12 form a circumferential outer cooling channel 19. The lower piston part 12 furthermore has a centric inner cooling cavity 21. The cooling cavity bottom 22 of the cooling cavity 21 is provided with an opening 23 approximately in the shape of an oblong hole in the exemplary embodiment (see FIGS. 2 and 3). The upper piston part 11 and the lower piston part 12 are connected with one another by way of an outer joining seam 24 and an inner joining seam 25, for example by means of a welding or soldering method. A cooling oil channel 26 is provided in the lower piston part 12 and connects the cooling channel 19 with the cooling cavity 21. The cooling oil channel 26 runs downward, at an angle, in the direction of the cooling cavity 21, proceeding from the cooling channel 19.

FIGS. 4 to 6 show in detail that the opening 23 in the cooling cavity bottom 22 is closed off with a closure element 33 that is configured essentially corresponding to the opening 23, in order to be able to reliably close it off. In the exemplary embodiment, the closure element 33 is produced from a spring sheet, approximately 0.8 mm thick, and held in the opening 23 in clamped manner. For this purpose, two engagement grooves 34 disposed in centered manner, lying opposite one another, are provided in the piston interior in the lower piston part 12, in the region of the opening 23. Instead, a single circumferential engagement groove can also be provided.

As is particularly evident from FIG. 4, in the exemplary embodiment the closure element 33 has an essentially rectangular base body 41 having a central opening 41 a. The shape of the base body 41 corresponds to the opening 23 in the cooling cavity bottom 22, in order to be able to reliably close this off. Two resilient engagement elements 37 are provided on the longitudinal sides of the base body 41, in each instance, which elements are disposed in pairs, diametrically opposite one another. The engagement elements 37, which are configured as engagement tongues in the exemplary embodiment, are separated from one another by means of slits 35 that extend radially inward and open into a rounded part 36, in each instance. A spring tab 38 is provided on the two transverse sides of the base body 41, in each instance. The spring tabs 38 are delimited, in their transition region to the base body 41, by slits 35 that extend radially inward and open into a rounded part 36. The slits 35 and the rounded parts 36 serve, together with the central opening 41 a, as cooling oil openings that allow the cooling oil to flow out of the inner cooling cavity 21 in the direction of the piston pin, during operation. The slits 35 and the rounded parts 36 are punched out of the closure element 33 in the exemplary embodiment.

For assembly, the closure element 33 is pushed into the opening 23 of the cooling cavity bottom 22 from the direction of the pin bores 17. In this connection, first the spring tabs 38 come to lie against a contact surface 39 in the interior of the piston 10. The contact surfaces 39 are configured in the region of the pin boss links 18, below the engagement grooves 34.

During the further course of assembly, the closure element 33 is pushed further in the direction of the cooling cavity 21, so that the spring tabs 38 have a bias applied to them. When the engagement elements 37 reach the engagement grooves 34, they at first give way, in resilient manner, and subsequently engage into the engagement grooves 34, maintaining the spring bias. The base body 41 of the closure element 33 then covers the opening 23 in the cooling cavity bottom 22 almost completely. If desired, a narrow gap 42 can remain between the base body 41 and the piston interior, which gap can serve as a further cooling oil opening (see FIG. 3).

In the end result, a spring bias is in effect, in the assembled state, between the spring tabs 38 and the engagement elements 37 of the closure element 33. This spring bias acts in the axial direction and stabilizes the closure element 33 in its seat, with regard to the forces that are in effect during the piston stroke. The spring bias can be adjusted, in known manner, by way of the thickness of the entire closure element 33 or individual ones of its regions and/or by way of beads introduced into the closure element 33 (not shown). 

1. Piston (10) for an internal combustion engine, having an outer circumferential cooling channel (19) and an inner cooling cavity (21), the cooling cavity bottom (22) of which has an opening (23) that is closed off with a separate closure element (33) that has at least one cooling oil opening (35), whereby the closure element (33) is held, in clamped manner, by means of two engagement elements (37) disposed on the outer edge, in at least one engagement groove (34) provided in the region of the opening (23) of the cooling cavity bottom (22), wherein the closure element (33) has at least two spring tabs (38) that support themselves on a contact surface (39) provided in the piston interior, in each instance, in such a manner that the closure element (33) is held in the engagement groove (34) under axial bias.
 2. Piston according to claim 1, wherein the spring tabs (38) support themselves on a contact surface (39) provided in the region of the pin boss links (18), in each instance.
 3. Piston according to claim 1, wherein the at least one engagement groove (34) is provided in the region of the pin boss links (18).
 4. Piston according to claim 1, wherein the at least two engagement elements (37) and/or the at least two spring tabs (38) lie diametrically opposite one another.
 5. Piston according to claim 1, wherein the engagement elements (37) are configured as engagement tongues.
 6. Piston according to claim 1, wherein the closure element (33) has two or more cooling oil openings (35).
 7. Piston according to claim 1, wherein the at least one cooling oil opening (35) in the closure element (33) is configured as a slit that extends radially inward from the edge of the closure element (33).
 8. Piston according to claim 1, wherein the engagement elements (34) and/or the spring tabs (38) are delimited by slits that extend radially inward from the edge of the closure element (33).
 9. Piston according to claim 1, wherein a narrow gap (42) is provided in the region of the spring tabs (38), between the piston interior and the closure element (33).
 10. Piston according to claim 1, wherein the opening (23) in the cooling cavity bottom (22) and the closure element (33) are essentially configured to be round.
 11. Piston according to claim 1, wherein the opening (23) in the cooling cavity bottom (22) is configured to be oval or as an oblong hole, and the closure element (33) is configured corresponding to this.
 12. Piston according to claim 1, wherein the closure element (33) is produced from a spring steel sheet.
 13. Piston according to claim 1, wherein it is configured as a two-part piston having an upper piston part (11) and a lower piston part (12). 